Electronic frequency-tuning mechanism

ABSTRACT

This invention is concerned with an electronic mechanism for tuning musical instruments and other frequency-generating devices, by means of a meter eliminating the necessity of a trained human ear. The mechanism provides means for feeding the input signal to a preamplifier; feeding the amplified signal to a clipper; feeding the output of the clipper to both a divider and to a differentiator; thence, to a selector switch which may be used to divide or multiply the frequency of the signal by powers of two. The signal is then fed to a standard pulse generator and from there to a meter circuit which may be of the D&#39;&#39;Arsonvaltype. The readings on the meter will indicate to the operator to what extent the frequency of the musical instrument is tuned since the mechanism is already calibrated in accordance with the position of the selector switch to a specific frequency.

United States Paten u a Glorroso et al.

Jan. 25, 1972 OTHER PUBLICATIONS Abbott; Western Electric Tech. DlG. No. 7; July, 1967; p. 39.

[72] Inventors: Robert M. Glorioso, 19 Mass Lane, Am- Prim Em i r Alf d E S h herst, Mass. 01002; H. Craig Brooks, 83 f g Sagamore Ave., Oceanport, NJ. 07757 y n [22] Filed: Mar. 4, 1970 [57] ABSTRACT [211 App]. No.: 16,089 This invention is concerned with an electronic mechanism for tuning musical instruments and other frequency-generating devices, by means of a meter eliminating the necessity of a ..324/78(l;l,)illl2g7lgil trained human ear. The mechanism provides means for feed ing the input signal to a preamplifier; feeding the amplified [58] Field ofSearch ..324/78 E, 78 D, 78 J, 78 Q Signal to a clipper; feeding the output ofthe clipper to both a divider and to a differentiator; thence, to a selector switch [56] References cued which may be used to divide or multiply the frequency of the UNITED STATES PATENTS signal by powers of two. The signal is then fed to a standard pulse generator and from there to a meter circuit which may 2,955,202 lO/l960 Scourtes ..324/78 E be of the DArsonval-type. The readings on the meter will in- 2,999,l68 9/1961 Henry ..324/78l dicate to the operator to what extent the frequency of the musical instrument is tuned since the mechanism is already FOREIGN PATENTS OR APPLICATIONS calibrated in accordance with the position of the selector 802,693 l0/l958 Great Britain ..324/l7l swlichwaspeclfic frequency- 4 Claims, 2 Drawing Figures INPUT DEVICE CLIPPER DlVlDElZ mvwrsz mvmse AMPHFIEI? DIFF EQENTIATOIZ DIFFEPENTIATOR TUNl N6 METER METER STANDARD P LSE cuzcun' GENERATOR I3 BEA*QAO Far G G* ELECTRONIC FREQUENCY-TUNING MECHANISM Our invention relates to an electronic mechanism for tuning musical instruments such as pianos, guitars, organs, and the like or electrical signal-generating devices to a specific frequency with a high degree of accuracy.

An object of our invention is to provide a visual readout which indicates to the operator the relative difference in frequency between the frequency of the device under test and the desired frequency to which same is being tuned.

Another object of our invention is to provide a means for selecting the frequency or tone to be tuned, enabling each note on a multiple stringed instrument to be tuned without requiring any special skills on the part of the operator.

It is another object of the within invention to provide an accurate mechanism for tuning musical instruments which is simple in operation and inexpensive to manufacture.

Another object of the invention is to provide a mechanism for tuning musical instruments of the type that have only a small number of basic frequencies, such as a guitar with six or a violin with four, as well as a piano with many basic frequencm.

The above objects are obtained by averaging a sequence of pulses derived from an electrical input sequence generated by the instrument or device. Either a microphone or other electrical transducer may be used to feed the musical tone under test into the mechanism. Because of the circuit arrangement in the mechanism, a pulse sequence is formed of a specific average value which is related to the frequency being tuned. This is obtained by means of an arrangement of a preamplifier, clipper, differentiator, pulse generator and meter circuit. There is a selector switch placing into the arrangement a divider or a multiplier circuit for translating the musical octaves to a specific range of frequencies. The output of the invention comprises a simple meter which indicates the relative and specific timing with respect to the correct frequency.

Reference is made to the following detailed specifications, in which:

FIG. 1 is a block diagram of the various component circuits comprising the electrical mechanism of this invention.

FIG. 2 is a specific schematic diagram of a mechanism for testing a small range of frequencies such as would be used to tune a guitar.

Referring to F 1G. 1, there is an input device 1 which may be an electronic signal-generating instrument, a microphone or other transducer, or an electrical musical instrument such as an electric guitar or organ. Input device 1 provides an electrical input signal to the preamplifier 2 which provides proper loading for the input device 1 as well as amplifying the signal to the amplitude level required to drive the clipper 3 which may be a Schmitt trigger or other clipping device. The clipper 3 provides a square wave signal of the same frequency and phase as the input device 1 at the output 15 of the clipper 3, and provides a square wave signal of the same frequency but with opposite phase from the input device 1 at output 16 of the clipper 3. Thus, when mechanically coupled switches S1 and S2 are in position X2, the clipper output at 15 drives a differentiator-clamping circuit which produces a single pulse of narrow width for every cycle of the input signal.

The other clipper output signal at 16 drives the second differentiator-clamping circuit 17 which also produces a single pulse of narrow width for every cycle of the input signal. The pulse from differentiator l7 differs in phase from the pulse from differentiator 10 by 180 because of the phase difference between clipper outputs at and at 16. Also, in this switch position X2 the logical OR-gate 11 is activated and thus produces two pulse outputs for every cycle of the input signal. This is a process of frequency doubling and provides a mechanism for tuning a device with an output which is one octave below some standard or particular frequency range.

Next, let us consider the operation when switches S1 and S2 are in position XI. The clipper output at 15 drives differentiator 10 which produces one pulse output for each cycle of the input signal. Here, the frequency of pulses from the differentiator is equal to that of the input signal.

The effect of placing switches S1 and S2 in position 2 is as follows:

The clipper 3 drives a divider 4 which may be a toggle flipflop so as to provide a square wave drive to the differentiator 10 with a frequency which is one-half of the frequency of the input signal. Thus, the differentiator 10 produces one output pulse for every two cycles of the input signal and frequency division has been realized.

Further, switch position 4 allows the use of a signal to drive the differentiator 10 which results from division of the input frequency by 2 with divider 4 and divided again by 2 by divider 5. Thus, differentiator 10 is driven by a square wave with a frequency which is one-fourth of the frequency of the input signal and the differentiator produces one pulse for every 4 cycles of the input signal. Switch position 4 then provides division of the input frequency by 4. Similarly, the other switch positions in conjunction with dividers 6, 7, 8 and 9d provide frequency division by 8, 16, 32 and 64 respectively.

In summary, the input pulses to the standard pulse generator 12 may be selected by means of mechanically coupled switches S, and S to be:

a. The same frequency as the input signal as in position X1 b. Twice the frequency of the input signal as in position X2 0. A frequency which is a division of the input frequency by powers of 2 as in positions 2 through 64.

Mechanically coupled switches S1 and S2 provide a mechanism for translating signals over a large frequency range, i.e., many octaves, to a particular frequency range or octave.

The standard pulse generator 12 may be one of several types of one-shot multivibrators or pulse generators in which the pulse width can be adjusted. A switch S4 is provided to select one of several standard pulse widths where each position is calibrated for the same average output value for each of the several tones to which a device is to be tuned. For example, the pulse generator may be calibrated to the following octave:

C#34.65 Hz. D36.71 Hz. Dil -38.89 Hz. Iii-41.20 Hz. F43.65 Hz. F #46.25 Hz. G49.00 Hz. G#51.91 Hz. A55.00 Hz. A#58.27 Hz. B61.74 Hz. C65.41 H5, 7

Thus, switches S1, S2 and S4 in conjunction with the standard pulse generator 12 may be used to translate any tone in a scale of 8 octaves to one of the tones in the above octave. Thus, each tone can be translated to a pulse train of the same average value, V The sequence of pulses from standard pulse generator 12 of average value V is fed into the meter circuit 13 which averages the pulse sequence, provides meter shunting and protection, and provides a means for shifting the meter reference. The meter reference, selected by switch S3 is used to select either a standard scale (A=440Hz.), position S, or another scale which is above or below the standard scale, position V. The output of the meter circuit is direct current which drives the tuning meter 14. The system is calibrated such that the given average value of the pulse train, V deflects the meter to center scale. Therefore, a pulse train of frequency lower than the desired frequency with a lower average value produces a direct current less than that required to deflect the meter to half scale and similarly a higher frequency deflects the meter above half-scale.

In order to tune a musical instrument or signal-generating device, the following takes place:

1. The appropriate electrical form of the tone or signal is applied to the input 1.

2. Switches S1, S2 are positioned to select the octave to which the instrument is to be tuned.

3. Switch S4 is used to select the desired note (tone) in that octave.

4. Switch S3 is placed in position S for standard pitch tuning or position V for nonstandard tuning. Nonstandard tuning is accomplished by adjusting resistor R14 such that the meter is at center scale for any one note in a nonstandard scale. For example, a note on a piano which is tuned slightly above or slightly below standard tune.

5. The instrument is then adjusted, for example, the strings of a stringed instrument are tightened or loosened, such that the meter is at center scale for the appropriate frequency or frequencies.

Reference is now made to FIG. 2, which is an embodiment of the invention for tuning a six-string instrument such as a guitar or other device which uses a small set of basic tones over a broad frequency range.

The appropriate signal from the guitar is applied to the transducer and fed to the preamplifier 2 which amplifies the signal to the level required to drive the clipper circuit 3 which may be a Schmitt trigger or other circuit which provides clipping with two outputs, one in phase with the input signal and the other of opposite phase from the input signal at 15 and 16 respectively. The inphase square wave signal 15 from the clipper 3 is applied to capacitor C1 which differentiates the square wave causing a narrow pulse to appear in time at the transitions of the square wave. Diode D1 provides a path to ground for positive pulses while negative pulses pass through D2 and are applied to the base of transistor T1. Thus, with switch S in position X1, one negative pulse per cycle of the input signal is applied to the base of T1. When switch S5 is in position X2, the out-of-phase square wave from the clipper 16 being shifted 180 from the input signal, is applied to capacitor C2 which differentiates the square wave as above except that a negative pulse is generated by C2 and then passes through D4 at the same time that a positive pulse is generated by C1. Thus, with S5 in the X2 position, two negative pulses appear at the base of T1 for each cycle of the input signal and frequency doubling is accomplished.

Transistor Tl along with transistors T2, T3 and T4 make up a realization of a standard pulse generator. Resistor R1 biases T1 on, under quiescent conditions, which causes the collector of T1 and the bases and emitters of T2 and T3 to be at ground potential. A negative pulse at the base of T1 causes it to turn off which increases the potential at the collector of T1 which biases transistor T2 on, through resistor R2. The emitter potential of transistors T2 and T3 also tend to increase, which biases transistor T4 on, through capacitor C3 and resistor R9, causing transistor T4 to turn on, which, in turn, causes the base of T1 to remain at a low potential and regeneration is implemented. As C3 becomes charged, T4 turns off, which turns TI on, and the pulse generator returns to its quiescent state; and C3 is rapidly discharged through D7 and T3. The amount of time that the emitters of T2 and T3 stay at the positive potential, Vcc, is determined by the time constant which, with Switch S6 in position E, is the product of R9 and C3. Thus, switch S6 is used to select the different resistors, R9, R10, R11, R12, R13 or R14, which produce different pulse widths to correspond to the tones or frequencies, E, A, D, G, B and E2 respectively, to which the device is to be tuned.

The pulse sequence from the low-impedance source, namely the emitters of T2 and T3, are passed through the averaging circuit resistor R3 and capacitor C4 of the meter circuit. The average value of the pulse sequence is then applied to the meter bias and shunt circuit consisting of the resistor R4, meter 25, diode D6, resistor R5, resistor R6, resistor R7, resister R8 and switch S7.

For tuning to a standard scale with A=440 l-lz., consider switch S7 in position S. Here R8, R5, and R7 form a voltage divider which places a voltage V at the junction of R5, R7 and D6. Thus, if the average value of the pulse sequence V is less than V,,, then diode D6 is back biased and no current flows through the meter 25. If the voltage V, is greater than the voltage V by the diode D6 voltage drop, then current flows through the meter 25. For a given difference Il -V the current which flows through the meter is determined by R4 plus the equivalent resistance of R5 and R8 in parallel with R7 plus the internal meter resistance. Thus, for each input frequency to be tuned the corresponding timing resistor is selected from R9-R14 at the appropriate switch position of S6 such that the average value of the pulse sequence causes the meter to be deflected to center scale, V =V The meter 25 then reads:

a. Below center scale if the input device is below the desired tuning frequency.

b. At center scale if the frequency is equal to the desired tuning frequency. I

c. Above center scale if the frequency is higher than the desired tuning frequency. 1

Diode D5 protects the meter 25 from being damaged when the input frequency is much greater than the desired tuning frequency i.e., when V is much greater than V,,.

Next, consider switch S7 in position V where R5 is replaced by variable resistor R6 in the voltage divider circuit. Resistor R5 allows the voltage V, to be varied thus changing the average value of the pulse sequence required for center scale meter deflection and therefore the relative calibration of the meter can be adjusted for a scale of tones above or below the standard scale.

The tuning device illustrated in FIG. 2 may be used to tune a guitar or bass as follows: A guitar is tuned by placing switch S5 in position X1, applying the appropriate input device, transducer, etc., and using switch S6 to tune each string as given below.

String number Note Frequency 1 5, 329.63 Hz. 2 B 246.94 Hz.

3 G l96.00 Hz. 4 D 6.83 Hz.

5 A 0.00 Hz.

6 E 82.41 Hz.

A has or bass guitar is tuned by placing switch S5 in position X2 which doubles the effective frequency of the input From the foregoing description it becomes apparent that this invention provides a mechanism for efficiently tuning or aligning musical instruments or signal generating devices to a specific frequency or set of frequencies. It is also clear that this invention provides a means of changing or selecting its calibration to some other than an internally set standard.

While the invention has been described in general and in a particular embodiment, it should be understood that it is not limited thereto, but may be carried out by other means within the spirit and scope of the following claims.

We claim:

1. A mechanism for measuring and determining the pitch of sound or the frequency of a musical instrument or a signal generator comprising an input device, a clipper circuit having an output, a switching means connected to said output, a first differentiator connected to said switching means, a standard pulse generator, the output of the said differentiator connected to said pulse generator, a meter circuit, said standard pulse generator having an output circuit, said output circuit connected to said meter circuit, said meter circuit connected to a meter, a divider circuit, said divider circuit connected to said clipper circuit, the output of said divider being connected to said switching means, whereby said switching means allows the selection of fundamental or subharmonic frequencies, said switching means being connected to said first differentiator, means for connecting the output of said difierentiator to a logical OR gate; said logical OR gate being connected to the input of said pulse generator, a second differentiator connected to a second output of the said clipper circuit of opposite phase from the first input, and to said OR gate, whereby two pulses are applied to the input of the pulse generator for every cycle of the input signal.

2. A mechanism as described in claim 1 having a plurality of divider circuits, said switching means connected to the output of said clipper circuit and said switching means connected to each of said plurality of divider circuits, and said switching means connected to said OR gate, each of said divider circuits being calibrated to divide by two the frequency of its input signal, whereby the operation of the switching means determines the octave or range of the frequency under test,

3. A mechanism as described in claim 2 wherein said meter circuit comprises an input, said input being connected to the output of the pulse generator, said input comprising a low-pass filter, a first diode connected also to the output of said lowpass filter, a resistor, a meter, said resistor connected to said meter, said first diode connected in parallel and across said resistor and said meter, whereby a nonlinear frequency scale at the upper end of said meter range is created, the output of said diode and said resistor-meter connected to a second diode, a source of voltage, said second diode having an output connected to said source of voltage, a variable means for controlling and presetting the voltage source whereby range selection is obtained and whereby the meter scale is adjusted to different readings to accommodate different frequencies.

4. A mechanism as described in claim 1 wherein said meter circuit comprise an input, said input being connected to the output of the pulse generator, said input comprising a low-pass filter, a first diode connected also to the output of said lowpass filter, a resistor, a meter, said resistor connected to said meter, said first diode connected in parallel and across said resistor and said meter, whereby a nonlinear frequency scale at the upper end of said meter range is created, the output of said diode and said resistor-meter connected to a second diode, a source of voltage, said second diode having an output connected to said source of voltage, a variable means for controlling and presetting the voltage source whereby range selection is obtained and whereby the meter scale is adjusted to different readings to accommodate different frequencies. 

1. A mechanism for measuring and determining the pitch of sound or the frequency of a musical instrument or a signal generator comprising an input device, a clipper circuit having an output, a switching means connected to said output, a first differentiator connected to said switching means, a standard pulse generator, the output of the said differentiator connected to said pulse generator, a meter circuit, said standard pulse generator having an output circuit, said output circuit connected to said meter circuit, said meter circuit connected to a meter, a divider circuit, said divider circuit connected to said clipper circuit, the output of said divider being connected to said switching means, whereby said switching means allows the selection of fundamental or subharmonic frequencies, said switching means being connected to said first differentiator, means for connecting the output of said differentiator to a logical OR gate; said logical OR gate being connected to the input of said pulse generator, a second differentiator connected to a second output of the said clipper circuit of opposite phase from the first input, and to said OR gate, whereby two pulses are applied to the input of the pulse generator for every cycle of the input signal.
 2. A mechanism as described in claim 1 having a plurality of divider circuits, said switching means connected to the output of said clipper circuit and said switching means connected to each of said plurality of divider circuits, and said switching means connected to said OR gate, each of said divider circuits being calibrated to divide by two the frequency of its input signal, whereby the operation of the switching means determines the octave or range of the frequency under test.
 3. A mechanism as described in claim 2 wherein said meter circuit comprises an input, said input being connected to the output of the pulse generator, said input comprising a low-pass filter, a first diode connected also to the output of said low-pass filter, a resistor, a meter, said resistor connected to said meter, said first diode connected in parallel and across said resistor and said meter, whereby a nonlinear frequency scale at the upper end of said meter range is created, the output of said diode and said resistor-meter connected to a second diode, a source of voltage, said second diode having an output connected to said source of voltage, a variable means for controlling and presetting the voltage source whereby range selection is obtained and whereby the meter scale is adjusted to different readings to accommodate different frequencies.
 4. A mechanism as described in claim 1 wherein said meter circuit compriSes an input, said input being connected to the output of the pulse generator, said input comprising a low-pass filter, a first diode connected also to the output of said low-pass filter, a resistor, a meter, said resistor connected to said meter, said first diode connected in parallel and across said resistor and said meter, whereby a nonlinear frequency scale at the upper end of said meter range is created, the output of said diode and said resistor-meter connected to a second diode, a source of voltage, said second diode having an output connected to said source of voltage, a variable means for controlling and presetting the voltage source whereby range selection is obtained and whereby the meter scale is adjusted to different readings to accommodate different frequencies. 